By The Nation
The victim was Amata Pinthong, 38, while the gunman was identified as Saranyoo Onjai-eua, 27.
The shooting occurred on Panit Road in Muang district on Tuesday while the two returned from the school where the ceremony was held for children to show gratitude to their fathers.
It was rumoured that Saranyu attacked Amata because he was angry that his ex-wife allowed Amata to sit in his place.
Because December 5 is a national holiday, the school held the ceremony one day in advance.
Amata reportedly drove through heavy traffic, hitting pavements and other vehicles in an attempt to reach a police station to seek help, as Saranyoo reportedly chased him on a motorcycle with a gun.
The gunman fled when the victim reached the station, it was reported.
Amata was shot in the back of the neck and treated at Buddhasothorn Hospital.
His younger brother, who was also in the car, escaped injury.
Lt Col Supan Polpakdee, deputy chief of Muang Chachoengsao police, said officers were seeking an arrest warrant for Saranyu.
Saranyu's relatives said he would turn himself in.